Bug 1579108 - Change the form in login-item to grid so that the copy buttons can reliably align r=sfoster,ntim

Implementing grid layout using flex may sometimes triggers edge cases where some columns go out of alignment. In this bug, the misalignment is due to the different length value given by -moz-available when Ubuntu font is used on the page.

Differential Revision: https://phabricator.services.mozilla.com/D100395

browser/components/aboutlogins/content/aboutLogins.html

@@ -264,8 +264,8 @@
                 <a class="origin-input" dir="auto" target="_blank" rel="noreferrer" name="origin" href=""></a>
               </label>
             </div>
+            <div class="detail-grid">
               <div class="detail-row">
-              <div class="detail-row-contents">
                 <label class="detail-cell">
                   <span class="username-label field-label" data-l10n-id="login-item-username-label"></span>
                   <input type="text"
@@ -279,9 +279,7 @@
                   <span class="copy-button-text" data-l10n-id="login-item-copy-username-button-text"></span>
                 </button>
               </div>
-            </div>
               <div class="detail-row">
-              <div class="detail-row-contents">
                 <label class="detail-cell">
                   <span class="password-label field-label" data-l10n-id="login-item-password-label"></span>
                   <div class="reveal-password-wrapper">

browser/components/aboutlogins/content/components/login-item.css

@@ -72,10 +72,10 @@ input[type="url"]:read-only {
   all: unset;
   font-size: 1.1em;
   display: inline-block;
-  width: -moz-available;
   background-color: transparent !important; /* override common.inc.css */
   text-overflow: ellipsis;
   overflow: hidden;
+  width: 100%;
 }
 
 /* We can't use `margin-inline-start` here because we force
@@ -154,17 +154,39 @@ input[type="url"]:read-only:hover:active {
   align-items: center;
 }
 
+.detail-grid {
+  display: grid;
+  grid-template-columns: minmax(240px, max-content) auto;
+  grid-template-rows: auto;
+  column-gap: 20px;
+  row-gap: 40px;
+  justify-content: start;
+}
+
+:host([data-editing]) .detail-grid {
+  grid-template-columns: auto;
+}
+
+.detail-grid > .detail-row:not([hidden]) {
+  display: contents;
+}
+
+.detail-grid > .detail-row > .detail-cell {
+  grid-column: 1;
+}
+
+.detail-grid > .detail-row > .copy-button {
+  grid-column: 2;
+  margin-inline-start: 0; /* Reset button's margin so it doesn't affect the overall grid's width */
+  justify-self: start;
+  align-self: end;
+}
+
 .detail-row {
   display: flex;
 }
 
-.detail-row-contents {
-  display: flex;
-  align-items: end;
-  flex-basis: 340px; /* Allows for 360px of flex on the end (700px (the default 100% width) - 340px) */
-  max-width: 100%;
-}
-
+.detail-grid,
 .detail-row,
 .form-actions-row {
   margin-bottom: 40px;
@@ -188,7 +210,6 @@ input[type="url"]:read-only:hover:active {
 
 .copy-button {
   margin-bottom: 0; /* Align button at the bottom of the row */
-  margin-inline-start: 20px;
 }
 
 .copy-button:not([data-copied]) .copied-button-text,